Retinal camera with dynamic illuminator for expanding eyebox

ABSTRACT

A dynamic illuminator includes a central aperture, a ring of inner light sources, a plurality of primary illumination arrays, and a plurality of secondary illumination arrays. The ring of inner light sources is arranged around the central aperture. The plurality of primary illumination arrays extends along radial axes from the central aperture outside of the ring of inner light sources, wherein the primary illumination arrays each includes a plurality of primary light sources. The plurality of secondary illumination arrays is disposed along secondary axes extending from the central aperture outside of the ring of inner light sources. The secondary illumination arrays each includes a plurality of secondary light sources. The secondary axes of the secondary illumination arrays are disposed angularly between adjacent ones of the primary illumination arrays.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/943,879, filed Jul. 30, 2020, which claims the benefit of U.S.Provisional Application No. 62/902,286, filed Sep. 18, 2019, both ofwhich are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This disclosure relates generally to retinal imaging technologies, andin particular but not exclusively, relates to illumination techniquesfor retinal imaging.

BACKGROUND INFORMATION

Retinal imaging is a part of basic eye exams for screening, fielddiagnosis, and progress monitoring of many retinal diseases.Conventional retinal cameras typically have a very limited eyebox due tothe need to block deleterious image artifacts. The eyebox for a retinalcamera is a three-dimensional region in space typically defined relativeto an eyepiece of the retinal camera and within which the center of apupil or cornea of the eye should reside to acquire an acceptable imageof the retina. The small size of conventional eyeboxes makes retinalcamera alignment difficult.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified. Not all instances of an element arenecessarily labeled so as not to clutter the drawings where appropriate.The drawings are not necessarily to scale, emphasis instead being placedupon illustrating the principles being described.

FIG. 1 illustrates a retinal imaging system with a dynamic illuminator,in accordance with an embodiment of the disclosure.

FIGS. 2A & 2B illustrate various views of a dynamic illuminator havingprimary illumination arrays and secondary illumination arrays extendingparallel to one another, in accordance with an embodiment of thedisclosure.

FIGS. 3A & 3B illustrate various views of a dynamic illuminator havingprimary illumination arrays and secondary illumination arrays extendingradially from a center of a central aperture, in accordance with anembodiment of the disclosure.

FIGS. 4A & 4B illustrate the illumination of an eye and the resultingincident light.

FIGS. 5A & 5B illustrate example areas of the dynamic illuminator whichwill adequately illuminate the retina of an eye of a user based on thepositioning of the eye of the user and example areas which will causeimage artifacts from corneal reflections based on the positioning of theeye of the user.

FIGS. 6A & 6B illustrate retinal images including image artifacts, inaccordance with an embodiment of the disclosure.

FIG. 7 is a flow chart illustrating operation of the retinal imagingsystem, in accordance with an embodiment of the disclosure.

DETAILED DESCRIPTION

Embodiments of a system, apparatus, and method of operation of a retinalcamera with a dynamic illuminator having an expanded eyebox aredescribed herein. In the following description numerous specific detailsare set forth to provide a thorough understanding of the embodiments.One skilled in the relevant art will recognize, however, that thetechniques described herein can be practiced without one or more of thespecific details, or with other methods, components, materials, etc. Inother instances, well-known structures, materials, or operations are notshown or described in detail to avoid obscuring certain aspects.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

High fidelity retinal images are important for screening, diagnosing,and monitoring many retinal diseases. To this end, reducing oreliminating instances of image artifacts that occlude or otherwisemalign portions of the retinal image is desirable.

FIG. 1 illustrates a retinal imaging system 100 with a dynamicilluminator, in accordance with an embodiment of the disclosure. Theillustrated embodiment of retinal imaging system 100 includes a dynamicilluminator 105, an image sensor 110, a controller 115, a user interface120, a display 125, an alignment tracker 130, and an optical relaysystem. The illustrated embodiment of the optical relay system includinglenses 135, 140, 145 and a beam splitter 150. The illustrated embodimentof dynamic illuminator 105 includes an inner baffle 155 surrounding acenter aperture and illumination arrays 165.

The optical relay system serves to direct (e.g., pass or reflect)illumination light 180 output from dynamic illuminator 105 along anillumination path through the pupil of eye 170 to illuminate retina 175while also directing image light 185 of retina 175 (i.e., the retinalimage) along an image path to image sensor 110. Image light 185 isformed by the scattered reflection of illumination light 180 off ofretina 175. In the illustrated embodiment, the optical relay systemfurther includes beam splitter 150, which passes at least a portion ofimage light 185 to image sensor 110 while also directing display light190 output from display 125 to eye 170. Beam splitter 150 may beimplemented as a polarized beam splitter, a non-polarized beam splitter(e.g., 90% transmissive and 10% reflective, 50/50 beam splitter, etc.),a dichroic beam splitter, or otherwise. The optical relay systemincludes a number of lenses, such as lenses 135, 140, and 145, to focusthe various light paths as needed. For example, lens 135 may include oneor more lensing elements that collectively form an eyepiece that isdisplaced from the cornea of eye 170 by an eye relief 195 duringoperation. Lens 140 may include one or more lens elements for bringingimage light 185 to a focus on image sensor 110. Lens 145 may include oneor more lens elements for focusing display light 190. It should beappreciated that the optical relay system may be implemented with anumber and variety of optical elements (e.g., lenses, reflectivesurfaces, diffractive surfaces, etc.).

The image sensor 110 may sense light in the visible spectrum and theinfrared spectrum. The image sensor 110 may include separate visiblelight and infrared image sensors, or a single image sensor capable ofsensing both visible and infrared light.

In one embodiment, display light 190 output from display 125 is afixation target or other visual stimuli. The fixation target not onlycan aid with obtaining alignment between retinal imaging system 100 andeye 170 by providing visual feedback to the patient, but may also givethe patient a fixation target upon which the patient can accommodatetheir vision. Display 125 may be implemented with a variety oftechnologies including a liquid crystal display (LCD), light emittingdiodes (LEDs), various illuminated shapes (e.g., an illuminated cross orconcentric circles), or otherwise.

Controller 115 is coupled to image sensor 110, display 125, dynamicilluminator 105, and alignment tracker 130 to choreograph theiroperation. The controller 115 may include logic that when executed bythe controller 115 causes the controller 115 to control the image sensor110, display 125, dynamic illuminator 105, and alignment tracker 130.

Controller 115 may include software/firmware logic executing on amicrocontroller, hardware logic (e.g., application specific integratedcircuit, field programmable gate array, etc.), or a combination ofsoftware and hardware logic. Although FIG. 1 illustrates controller 115as a distinct functional element, the logical functions performed bycontroller 115 may be decentralized across a number of hardwareelements. Controller 115 may further include input/output (I/O ports),communication systems, or otherwise. Controller 115 is coupled to userinterface 120 to receive user input and provide user control overretinal imaging system 100. User interface 120 may include one or morebuttons, dials, feedback displays, indicator lights, etc.

Image sensor 110 may be implemented using a variety of imagingtechnologies, such as complementary metal-oxide-semiconductor (CMOS)image sensors, charged-coupled device (CCD) image sensors, or otherwise.In one embodiment, image sensor 110 includes an onboard memory buffer orattached memory to store retinal images.

Alignment tracker 130 operates to track alignment between retinalimaging system 100 and eye 170, including a gaze direction 171 of theeye 170. The alignment tracker 130 may operate using a variety ofdifferent techniques to track the relative positions of eye 170 and theretinal imaging system 100 including pupil tracking, retina tracking,iris tracking, or otherwise. These various tracking techniques may beused by the retinal imaging system 100 to determine the relativeposition of the eye 170 to the retinal imaging system as well as thegaze direction 171 of the eye 170. In one embodiment, alignment tracker130 is a gaze tracking camera that includes one or more infrared (IR)emitters to track eye 170 via IR light.

During operation, controller 115 operates dynamic illuminator 105 andimage sensor 110 to capture one or more retinal images. Dynamicilluminator 105 is dynamic in that its illumination pattern is notstatic; but rather, is dynamically changed under the influence ofcontroller 115 based upon the determined alignment with eye 170(discussed in detail below). Illumination light 180 is directed throughthe pupil of eye 170 to illuminate retina 175. The scattered reflectionsfrom retina 175 are directed back along the image path through anaperture in inner baffle 155 to image sensor 110. Inner baffle 155operates to block deleterious reflections and light scattering thatwould otherwise malign the retinal image while passing the image lightitself through the central aperture defined by the inner baffle 155. Theillumination patterns output by dynamic illuminator 105 are selectedbased upon the current alignment to reduce deleterious image artifacts.Image artifacts may arise from light scattering by the human lens withineye 170, reflections from the cornea/iris, or even direct specularreflections of illumination light 180 from retina 175. Direct specularreflections from retina 175 or the cornea/iris can create washed outregions in the retinal image. The dynamic changes in the illuminationpatterns output from dynamic illuminator 105 serve to direct thesespecular reflections off axis from the image path and therefore blockedby the inner baffle 155.

FIGS. 2A & 2B illustrate various views of a dynamic illuminator 200having primary illumination arrays 220 and secondary illumination arrays230 (only a portion are labelled) extending parallel to one another, inaccordance with an embodiment of the disclosure. The dynamic illuminator200 may be an example of the dynamic illuminator 105 illustrated in FIG.1 . As illustrated in FIG. 2A, the dynamic illuminator 200 may include aring of inner light sources 240, primary illumination arrays 220,secondary illumination arrays 230, inner baffle 212, outer baffle 214,and body 250.

The ring of inner light sources 240, the primary illumination arrays220, the secondary illumination arrays 230, the inner baffle 212, andthe outer baffle 214 may be mounted on or otherwise connected to thebody 250. In some embodiments the ring of inner light sources 240, theprimary illumination arrays 220, and the secondary illumination arrays230 may be mounted to the body 250 in a single plane. In otherembodiments, the ring of inner light sources 240, the primaryillumination arrays 220, and the secondary illumination arrays 230 maybe mounted to the body 250 in different planes or with individual LEDsin different planes (different distances from the eye 170).

The inner baffle 212 may define a central opening in the dynamicilluminator 200. The outer baffle 214 may be located between the ring ofinner light sources 240 and the primary and secondary illuminationarrays 220, 230. The ring of inner light sources 240, the primaryillumination arrays 220, and the secondary illumination arrays 230 maybe disposed on or in the body 250. In one embodiment, body 250 is amonolithic housing structure. In other embodiments, body 250 may befabricated from multiple components that connect together. Body 250 maybe fabricated from plastic, metal, or otherwise.

The inner baffle 212 and outer baffle 214 strategically cast shadowsonto eye 170 to confine the divergence pattern of the illumination fromthe ring of inner light sources 240. When the eye is in perfectalignment, the shadows cast by the inner baffle 212 and outer baffle 214will cast a shadow on the center of the corneal plane and lens of theeye 170 to reduce deleterious reflections at the cornea and lens.

The ring of inner light sources 240 may include several inner lightsources 245. For example, as illustrated in FIG. 2A the ring of innerlight sources 240 may include eight inner light sources 245. Otherexample embodiments may include 4 or more inner light sources 245. Theinner light sources 245 may be arranged in a ring around the centralopening defined by the inner baffle 212 with each inner light source 245having the same radial distance from a center of the central opening.The inner light sources 245 may be evenly spaced around the centralopening. Each inner light source 245 may include a visible light source241 and a pair of infrared light sources 242 on either side of thevisible light source 241. The illumination of the ring of inner lightsources 240 including individual control of the individual visible lightsources 241 and infrared light sources 242 may be controlled by thecontroller 115.

The primary illumination arrays 220 may be arranged around the centralaperture, such that the primary illumination arrays 220 extends alongradial axes from the central aperture outside of the ring of inner lightsources 240. As illustrated in FIG. 2A, the dynamic illuminator 200 mayinclude eight primary illumination arrays 220. Other embodiments with adifferent number of primary illumination arrays 220 are also possible.Each primary illumination array 220 may extend in a direction radiallyoutward from the center of the central aperture and may be evenly spacedaround the center of the central aperture. Each of the inner lightsources 245 of the ring of inner light sources 240 may share a commonpolar angle as one of the radial axes of the primary illumination arrays220.

Each primary illumination array 220 may consist of multiple primarylight sources 225. The primary illumination array 220 may include fourprimary light sources 225. The primary illumination array 220 in otherexample embodiments may include a different number of primary lightsources 225. Each primary light source 225 may include a visible lightsource 221 and a pair of infrared light sources 222 on either side ofthe visible light source 221. Each primary light source 225 may have adifferent radial distance from the center of the central aperture. Theillumination of primary light sources 225 including individual controlof the individual visible light sources 221 and infrared light sources222 may be controlled by the controller 115.

Each secondary illumination array 230 may be arranged next to one of theprimary illumination arrays 220 (or proximate primary illumination array220) on the body 250. As illustrated in FIG. 2A, the dynamic illuminator200 may include eight secondary illumination arrays 230. Otherembodiments with a different number of secondary illumination arrays 230are also possible. The secondary illumination arrays 230 may be disposedalong secondary axes extending from the central aperture outside of thering of inner light sources 240. The secondary axes of the secondaryillumination arrays 230 are disposed angularly between adjacent ones ofthe primary illumination arrays 220. Restated, each secondaryillumination array 230 may extend in a direction away from the centralaperture and parallel to the proximate primary illumination array 220.Each secondary illumination array may extend away from the centralaperture but not radially outward from the center of the centralaperture. The secondary illumination array 230 may include threesecondary light sources 235. In other example embodiments, the secondaryillumination array 230 may include a different number of secondary lightsources 235. Each of the secondary light sources 235 are offset from theprimary light sources 225 to have a radial distance from a center of thecentral aperture different from that of each of the primary lightsources in the proximate primary illumination arrays 220. Accordingly,secondary light sources 235 provide intermediate spacing between theadjacent primary light sources 225. This intermediate spacing has asmaller pitch than the physical size of primary light sources 225 wouldotherwise permit when organized in a straight line. As such, secondarylight sources 235 provide increased granularity for selecting thelocation of illumination during retinal imaging.

Each secondary light source 235 may include a visible light source 231and a pair of infrared light sources 232 on either side of the visiblelight source 231. Each secondary light source 235 in one of thesecondary illumination arrays 230 may have a different radial distancefrom the center of the central aperture. The radial distance from thecenter aperture of each of the secondary light sources 235 may bebetween two of the radial distances between two of the primary lightsources 235 of the proximate primary illumination array 220. Restated,each secondary light source 235 may have a different radial distancefrom the center of the central aperture than the primary light sources225 in the proximate primary illumination array 220. The illumination ofsecondary light sources 235 including individual control of theindividual visible light sources 231 and infrared light sources 232 maybe controlled by the controller 115. Illumination light 180 may comefrom any of the visible light sources, 221, 231, 241 or a combination ofthe visible light sources 221, 231, 241. The visible light sources 221,231, 241 may be white light LEDs. The infrared light sources 222, 232,242 may be infrared LEDs.

FIG. 2B illustrates the dynamic illuminator 200 from a different pointof view. As illustrated, the outer baffle 214 is shorter than the innerbaffle 212. The primary and secondary light sources 225, 235 may bedisposed in cavities in the body 250. These cavities also form lightbaffles for constraining the divergence pattern of each light sourceexternal to outer baffle 214.

FIGS. 3A & 3B illustrate various views of a dynamic illuminator 300having primary illumination arrays 320 and secondary illumination arrays330 extending radially from a center of a central aperture, inaccordance with an embodiment of the disclosure. The dynamic illuminator300 may be another example of the dynamic illuminator 115 illustrated inFIG. 1 . The dynamic illuminator 300 is similar to the dynamicilluminator 200 except that the secondary illumination arrays 330 extendradially from the center of the central aperture rather than parallel toone of the primary illumination arrays 320.

Accordingly, the body 350, inner baffle 312 and outer baffle 314 may besimilar to the body 250, inner baffle 212, and outer baffle 214,respectively. The ring of inner light sources 340, inner light sources345, visible light sources 341 and infrared light sources 342 may besimilar to the ring of inner light sources 240, inner light sources 245,visible light sources 241 and infrared light sources 242, respectively.The primary illumination arrays 320, primary light sources 325, visiblelight sources 321 and infrared light sources 322 may be similar to theprimary illumination arrays 220, primary light sources 225, visiblelight sources 221 and infrared light sources 222, respectively. Thesecondary illumination arrays 330, secondary light sources 335, visiblelight sources 331 and infrared light sources 332 may be similar to thesecondary illumination arrays 230, secondary light sources 235, visiblelight sources 231 and infrared light sources 232, respectively, exceptfor their location on the body 350.

The secondary illumination arrays 330 may be arranged to extend alongsecondary axes radially outward from the center of the central aperture.Each secondary illumination array 330 may be evenly spaced between twoof the primary illumination arrays 320 (proximate primary illuminationarrays 320). Restated, the primary illumination arrays 320 and thesecondary illumination arrays 330 are angularly evenly spaced around thecentral aperture. Each secondary illumination array 330 may consist ofmultiple secondary light sources 335. Each secondary light source 335may include a visible light source 331 and a pair of infrared lightsources 332 on either side of the visible light source 331. Eachsecondary light source 335 in one of the secondary illumination arrays320 may have a different radial distance from the center of the centralaperture. The radial distance from the center aperture of each of thesecondary light sources 335 may be between two of the radial distancesof the primary light sources 335 of the proximate primary illuminationarrays 320. Restated, each secondary light source 235 may have adifferent radial distance from the center of the central aperture thanthe primary light sources 325 in the proximate primary illuminationarrays 320. The illumination of secondary light sources 335 includingindividual control of the individual visible light sources 331 andinfrared light sources 332 may be controlled by the controller 115.Illumination light 180 may come from any of the visible light sources,321, 331, 341 or a combination of the visible light sources 321, 331,341.

FIGS. 4A & 4B illustrate the illumination of an eye 170 and theresulting incident light. As illustrated in FIG. 4A, in order toilluminate the retina, the illumination light 405 passes through thecorneal plane, iris plane, and lens. The image light 403 also passesthrough the lens, iris plane, and corneal plane as it leaves the eye170. As the illumination light 405 passes through the corneal plane,iris plane, and lens, deleterious reflections may result. Thesedeleterious reflections may cause portions of the image captured by theimage sensor 110 to be washed out or otherwise unusable. Reflections offof the corneal plane may be of particular concern.

FIG. 4B shows how the illumination light 405 may cause a reflection 407which may wash out a portion of the image from the image light 403 ifthe reflection 407 overlaps with the illumination light when received bythe image sensor 110. The angle at which the illumination light 407passes through the corneal plane determines whether the reflection 407overlaps with the image light or not.

FIGS. 5A & 5B illustrate example areas of the dynamic illuminator 200which will adequately illuminate the retina 175 of an eye of a userbased on the positioning of the eye 170 of the user and example areaswhich will cause image artifacts from corneal reflections based on thepositioning of the eye of the user. The dynamic illuminator 200 is usedfor example purposes. The description of the areas of the dynamicilluminator 200 applies equally to dynamic illuminator 300 or otherexample embodiments.

As stated above, the angle at which the illumination light 407 entersthe corneal plane determines if the reflection 407 will overlap with theimage light 403. The angle at which the illumination light 407 passesthrough the pupil will determine if the entire retina 175 issufficiently illuminated for retina imaging. The alignment of the eye170 with the retinal imaging system 100 will cause light emitted from avisible light source 221, 231, 241 at certain areas of the dynamicilluminator 105 to illuminate the retina 175 to different degrees. Forexample, a visible light source 221, 231, 241 in the full illuminationarea 504 will fully illuminate the retina 175, while visible lightsource 221, 231, 241 in other areas will only partially illuminate theretina 175. Accordingly, it is possible to completely illuminate theretina 175 with only one visible light source 221, 231, 241. If the eye170 moves, the full illumination area 504 will move in a correspondingmanner and different visible light sources 221, 231, 241 could fullyilluminate the retina 175.

The alignment of the eye 170 with the retinal imaging system 100 willcause light emitted from a visible light source 221, 231, 241 at certainareas of the dynamic illuminator 105 to cause reflections which wash outportions of the retina 175. These reflections are examples ofdeleterious image artifacts. For example, a visible light source 221,231, 241 in the reflection area 502 may cause a reflection off thecorneal plane of the eye 170 that overlaps with the image light 403. Thesize and shape of the full illumination area 504 and the reflection area502 are determined by the shape and size of the eye 170 and thealignment of the eye 170 with the retinal imaging system 100.

FIG. 5A illustrates the case where the eye 170 is in perfect alignmentwith the retinal imaging system 100. In this case, the full illuminationarea 504 and the reflection area 502 are in the central aperture and nolight source may fully illuminate the retina 175. However, a combinationof the light from all of the visible light sources 241 in the ring ofinner light sources 240 can together illuminate the retina 175. Insimilar cases of near perfect alignment (minor misalignment), thevisible light sources 241 in the ring of visible light sources 240 cantogether illuminate the retina 175 without a reflection in the imagecaptured by the image sensor 110, as long as the reflection area 502does not overlap with any of the visible light sources 241. The innerbaffle 212 and the outer baffle 214 causes the reflection area 502 to besmaller for the ring of inner light sources 240 than for the primary andsecondary light sources 225, 235.

As illustrated in FIG. 5A, the closer the eye 170 is to perfectalignment the closer the full illumination area 504 and the reflectionarea 502 are to being concentric circles in the center of the dynamicilluminator 105 (aligning with the center of the central aperture). Asalignment shifts away from perfect, the shape and location of the fullillumination area 504 and the reflection area 502 changes.

Misalignment can lead to deleterious corneal reflections, refractivescattering from the crystalline lens, and occlusion of the imagingaperture. Conventional imaging systems have relatively small eyeboxes,which require precise alignment to avoid image artifacts from enteringthe image path. The dynamic illuminator 200, 300 combines two differentillumination architectures—one when the eye is roughly aligned with theoptical axis or gaze direction of the eye (ring of inner light sources240, 340) and one when the eye is offset from the optical axis or gazedirection of the eye (primary and secondary illumination arrays 220,320, 230, 330). By dynamically switching between these two illuminationarchitectures, the eyebox of the retinal imaging system described hereinmay be expanded by 2× or more over conventional ring illuminators.

As the eye 170 shifts in a transverse direction relative to the retinalimaging system 100, the full illumination area 504 and the reflectionarea 502 may shift in a transverse direction. Also, the relativemovement of the full illumination area 504 and the reflection area 502may be different such that the full illumination area 504 shifts morethan the reflection area 502. This type of misalignment may be correctedmanually by adjusting the retinal imaging system 100 or by theillumination processes described below.

As illustrated in FIG. 5B, in the case where the eye 170 is out ofposition angularly (such that the pupil is not directed exactly at thecentral aperture), the shape of the full illumination area 504 and thereflection area 502 may move away from the center of the centralaperture and elongate in a direction perpendicular to the directiontoward the center of the central aperture. This type of misalignment canbe difficult to adjust for by manually adjusting the retinal imagingsystem 100 because a person's eye moves constantly even when the personis trying to keep the eye focused on a single location.

The primary and secondary image arrays 220, 230 may be used tocompensate for either type of misalignment (transverse or angular). Theprimary and secondary light sources 225, 235 are arranged in order tohave one visible light source 221, 231 in the full illumination area 504and not in the reflection area 502 for any moderate misalignment causedby the ordinary movements of the eye 170 with a pupil size of about fourto ten millimeters. The area of the full illumination area 504 outsideof the reflection area 502 may be relatively small compared to thepractical limits on the distances between LEDs operating at the requiredpower levels. Further, because, the illumination area extends in adirection perpendicular to the direction to the center of the centralaperture, the radial distance to the center of the central aperturebecomes more important than the radial angle of the light source. Thus,the first light sources 225 and second light sources 235 have differentradial distances to the center of the central aperture so that at leastone of the visible light sources 221, 231 is within the fullillumination area 504 and outside of the reflection area 502.

FIG. 5B includes first, second, third, and fourth primary light sources225A, 225B, 225C, 225D, and first, second, and third secondary lightsources 235A, 235B, 235C. As is illustrated in FIG. 5B, the first andsecond primary light sources 225A, 225B are within the reflection area502. The third and fourth primary light sources 225C, 225D are outsideof the full illumination area and would only provide partialillumination of the retina 175. However, second secondary light source235B is in the full illumination area 504 and not in the reflection area502. Accordingly, it may be possible to achieve adequate illumination ofthe retina 175 without any corneal reflection from the second secondarylight source 235B. Thus, a moderate misalignment may be compensated forby using the second secondary light source 235B.

FIGS. 6A & 6B illustrate retinal images including image artifacts, inaccordance with an embodiment of the disclosure. FIG. 6A illustrates anexample retinal image 601 taken in visible light with one of the visiblelight sources 221, 231, 241 with an image artifact 605. The imageartifact 605 may arise when misalignment between the retinal imagingsystem and the eye permit stray light and deleterious reflections fromthe visible light sources 221, 231, 241 to enter the image path andultimately are captured by the image sensor with the retinal imagelight.

FIG. 6B illustrates an example infrared retinal image 602 taken ininfrared light with a pair of the infrared light sources 222, 232, 242from the same light source as the visible light source 221, 231, 241from FIG. 6A with image artifacts 607. As can be seen, the artifacts 607in the infrared retinal image 602 are in roughly the same area of theinfrared image 602 as the artifact 605 in the retinal image 601.Accordingly, the location of artifacts 607 in an infrared retina image602 is indicative of where an artifact 605 may appear in a retinal image601 in visible light (between the artifacts 607 in the infrared retinalimage 602).

Infrared is not visible to the human eye. Accordingly, the eye does notreact to infrared in the same way as visible light (for example, closingof eyelids, restricting pupil size, or looking away). Accordingly,taking retina images in infrared light combined with rapid imageprocessing may be used to determine if a visible light source 221, 231,241, 321, 331, 341 may be used to image the retina 175 in visible lightwith adequate illumination and without deleterious image artifacts.

FIG. 7 is a flow chart illustrating a process 700 for operation ofretinal imaging system 100, in accordance with an embodiment of thedisclosure. The order in which some or all of the process blocks appearin process 700 should not be deemed limiting. Rather, one of ordinaryskill in the art having the benefit of the present disclosure willunderstand that some of the process blocks may be executed in a varietyof orders not illustrated, or even in parallel. The process 700 may becontrolled by the controller 115.

In a process block 705, the retinal imaging process is initiated.Initiation may include the user selecting a power button from userinterface 120. In a process block 710, alignment tracker 130 commencestracking and determining the alignment between retinal camera system 100and eye 170. In particular, tracking may be determined as a relativemeasurement between eyepiece lens 135 and the pupil, iris, or retina ofeye 170. A variety of different alignment tracking techniques may beimplemented including pupil tracking, iris tracking, retinal tracking,trial and error, etc. The alignment tracking is used to determine whichof the illumination schemes should be used for illuminating retina 175during image acquisition. The transition between these illuminationschemes may be abrupt or a smooth fading therebetween as the relativealignment wanders between a central alignment and an offset alignment.

In decision block 715, if retinal camera system 100 is determined to becentrally aligned with the gaze direction 171 (e.g., optical axis of eye170) within a defined threshold, then process 700 continues to a processblock 720. The alignment may be determined to be centrally aligned byusing the alignment tracker to determine the general alignment of theeye 170 and/or capturing an infrared image using the infrared lightsources 242, 342 to illuminate the retina 175. If an image analysis ofthe image shows that the retina 175 is fully illuminated without anydeleterious inclusions then the controller 115 may determine that theretinal camera system 100 is centrally aligned with the gaze direction171.

In process block 720, dynamic illuminator 105 is operated by controller115 to generate a circular illumination pattern for illuminating retina175 through the pupil of eye 170 by turning on all of the inner lightsources 245, 345 of the ring of inner light sources 240, 340.

The emission divergence patterns of visible light sources 241, 341 areconstrained and controlled by inner and outer baffles 212, 312, 214, 314and a shadow cast by inner baffle 212, 312. Inner baffle 212, 312 servesto block the portion of the illumination light output from visible lightsources 241, 341 that would cause deleterious scattering in eye 170.Inner baffle 305 strategically casts an illumination shadow onto eyestructures that cause reflections (perpendicular portion of cornealplane and lens) to reduce image artifacts captured by image sensor 110.

In process block 730, the retinal image passes through the centralaperture defined by the inner baffle 212, 312 while the inner baffle212, 312 further blocks deleterious reflections and other strayrefractions. Then, in the process block 740, the image sensor 110acquires image light 185 forming the retinal image. The operations ofprocess blocks 720, 730, and 740 may be performed several times. Orrestated, several retinal images may be captured in quick succession.Generally 6 to 20 images can be captured before the eye 170 reacts tothe bright flash of the visible light sources. Accordingly, theoperations of process blocks 720, 730, and 740 may be performed up toabout 20 times in a row.

In process block 750, the controller may process the retinal image (orretinal images) to ensure adequate image quality. For example, imageprocessing may be done to check for adequate illumination of the retinaand for deleterious image artifacts. During image processing the retinalimages may be combined (e.g. image stacking) to exclude deleteriousimage inclusions from the retinal images.

Returning to decision block 715, if retinal camera system 100 isdetermined to be offset from the gaze direction 171 by a definedthreshold (a moderate misalignment), then process 700 continues toprocess blocks 760. In process blocks 760, the direction and amount ofoffset is estimated using the infrared light sources 222, 232, 322, 332.The direction and amount of offset may be estimated in several differentways.

As a first example, the alignment tracker 130 may detect the directionof the offset of the gaze of the user. The infrared light sources 222,322, 232, 332 of the primary and secondary light sources 225, 325, 235,335 in the detected direction of offset may then be used to captureinfrared retinal images to determine which of the primary and secondarylight sources 225, 325, 235, 335 may provide adequate illumination ofthe retina 175 without deleterious image artifacts in the visualspectrum.

As a second example, the infrared retinal image taken in process block710 may be used to determine the direction of the offset by analyzingthe illumination pattern of the retinal image. Then, the infrared lightsources 222, 322, 232, 332 of the primary and secondary light sources225, 325, 235, 335 in the determined direction of offset may then beused to capture infrared retinal images to determine which of theprimary and secondary light sources 225, 325, 235, 335 may provideadequate illumination of the retina 175 without deleterious imageartifacts in the visual spectrum.

As a third example, a method of guess and check using the infrared lightsources 222, 322, 232, 332 of the primary and secondary light sources225, 325, 235, 335 may be used to estimate the direction and amount ofoffset.

At process block 770, the captured infrared retinal images may beprocessed by the controller 115 in order to determine which visiblelight sources 221, 321, 231, 331 of the primary and secondary lightsources 225, 325, 235, 335, may provide adequate illumination of theretina 175 in the visual spectrum without deleterious image artifacts.Some differences in illumination and image artifacts will exist betweenretinal images captured using the infrared light sources 222, 322, 232,332 and the visible light sources 221, 321, 231, 331 even for the sameone of the primary and secondary light sources 225, 325, 235, 335. Also,as stated above, the human eye constantly moves. Further, as statedabove, generally 6 to 20 retinal images may be captured in visible lightbefore the eye reacts to visible light. Accordingly, the controller 115may determine to first capture a retinal image using visible lightillumination from one of the primary and secondary light sources 225,325, 235, 335. The controller 115 may also determine which other primaryand secondary light sources 225, 325, 235, 335 to use to capturesubsequent images in rapid succession. For example, the controller 115may determine to capture retinal images from each of the primary lightsources 225, 325 in one of the primary illumination arrays 220, 320 andeach of the secondary light sources 235, 335 of one of the secondaryillumination arrays 230, 330. The controller 115 may also determine tocapture multiple retinal images using one of the primary and secondarylight sources 225, 325, 235, 335.

Alternatively or additionally, the controller 115 may determine tocapture retinal images using multiple of the primary and secondary lightsources 225, 325, 235, 335. For example, multiple of the primary andsecondary light sources 225, 325, 235, 335 in different primary andsecondary illumination arrays 220, 320, 230, 330 may be used tocompensate for inadequate illumination of the retina from a singleprimary or secondary light source 225, 325, 235, 335. Restated, thecontroller 115 may determine to use a combination of primary andsecondary light sources 225, 325, 235, 335 to illuminate the retina 175while capturing a retinal image.

In process block 780 the dynamic illuminator 105 is operated bycontroller 115 to generate an illumination pattern (using one or more ofthe primary and secondary light sources 225, 325, 235, 335) forilluminating retina 175 through the pupil of eye 170. The image lightthen passes through the central aperture, at process block 730. Atprocess block 740, the image sensor 110 is also controlled by thecontroller 115 to capture the retinal image(s). Multiple retinal imagesmay be captured in quick succession.

At process block 750, the controller 115 may process the retinalimage(s) to determine if any of the retinal images have adequateillumination of the retina without deleterious image artifacts. Thecontroller 115 may also combine retinal images together to removedeleterious image artifacts or fill in areas of the retinal image withinadequate illumination.

The processes explained above are described in terms of computersoftware and hardware. The techniques described may constitutemachine-executable instructions embodied within a tangible ornon-transitory machine (e.g., computer) readable storage medium, thatwhen executed by a machine will cause the machine to perform theoperations described. Additionally, the processes may be embodied withinhardware, such as an application specific integrated circuit (“ASIC”) orotherwise.

A tangible machine-readable storage medium includes any mechanism thatprovides (i.e., stores) information in a non-transitory form accessibleby a machine (e.g., a computer, network device, personal digitalassistant, manufacturing tool, any device with a set of one or moreprocessors, etc.). For example, a machine-readable storage mediumincludes recordable/non-recordable media (e.g., read only memory (ROM),random access memory (RAM), magnetic disk storage media, optical storagemedia, flash memory devices, etc.).

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific embodimentsdisclosed in the specification. Rather, the scope of the invention is tobe determined entirely by the following claims, which are to beconstrued in accordance with established doctrines of claiminterpretation.

What is claimed is:
 1. An apparatus, comprising: a housing body having acentral aperture passing through the housing body; a plurality ofprimary cavities disposed in the housing body and arranged into primarycavity arrays that extend along radial axes from the central aperture,wherein the primary cavities are associated with primary light sourcesof an illuminator; and a plurality of secondary cavities disposed in thehousing body and arranged into secondary cavity arrays that extend alongsecondary axes from the central aperture, wherein the secondary cavitiesare associated with secondary light sources of an illuminator, whereinthe secondary axes of the secondary cavity arrays are disposed angularlybetween adjacent ones of the primary cavity arrays, and wherein each ofthe secondary cavities are offset from the primary cavities to have aradial distance from a center of the central aperture different fromthat of each of the primary cavities in the adjacent ones of the primarycavity arrays.
 2. The apparatus of claim 1, wherein the primary lightsources are disposed in or aligned with the primary cavities and thesecondary light sources are disposed in or aligned with the secondarycavities.
 3. The apparatus of claim 1, further comprising: an innerbaffle extending from the housing body and encircling the centralaperture.
 4. The apparatus of claim 3, further comprising: a ring ofinner cavities disposed in the housing body and arranged around thecentral aperture, the inner cavities associated with inner lightsources; and an outer baffle disposed radially exterior to the ring ofinner cavities and further disposed between the ring of inner cavitiesand the primary and secondary cavity arrays, wherein the outer baffle isshorter than the inner baffle.
 5. The apparatus of claim 4, wherein eachof the inner cavities of the ring of inner cavities shares a commonpolar angle with one of the radial axes of the primary cavity arrays. 6.The apparatus of claim 4, wherein the ring of inner cavities includeseight inner cavities, the primary cavity arrays include eight primarycavity arrays, and the secondary cavity arrays include eight secondarycavity arrays.
 7. The apparatus of claim 1, wherein each of thesecondary axes is parallel to but offset from one of the radial axes ofthe primary cavity arrays such that the secondary axes do not runradially from the center of the central aperture.
 8. The apparatus ofclaim 1, wherein the secondary axes each extend radially from the centerof the central aperture.
 9. The apparatus of claim 8, wherein theprimary cavity arrays and the secondary cavity arrays are angularlyevenly spaced around the central aperture.
 10. An apparatus for use witha retinal imager, the apparatus comprising: a housing structure having acentral aperture passing through the housing structure, the centralaperture adapted to optically align with an image sensor of the retinalimager; a plurality of primary light baffles disposed in the housingstructure and arranged into primary baffle arrays that extend alongradial axes from the central aperture, wherein the primary light bafflesare adapted to output first light emitted from primary light sources ofthe retinal imager; and a plurality of secondary light baffles disposedin the housing structure and arranged into secondary baffle arrays thatextend along secondary axes from the central aperture, wherein thesecondary light baffles are adapted to output second light emitted fromsecondary light sources of the retinal imager, wherein the secondaryaxes of the secondary baffle arrays are disposed angularly betweenadjacent ones of the primary baffle arrays, and wherein each of thesecondary light baffles are offset from the primary light baffles tohave a radial distance from a center of the central aperture differentfrom that of each of the primary light baffles in the adjacent ones ofthe primary baffle arrays.
 11. The apparatus of claim 10, wherein theprimary light sources are disposed in or aligned with the primary lightbaffles and the secondary light sources are disposed in or aligned withthe secondary light baffles.
 12. The apparatus of claim 10, furthercomprising: an inner light baffle extending from the housing structureand encircling the central aperture.
 13. The apparatus of claim 12,further comprising: a ring of inner light baffles arranged around thecentral aperture; and an outer baffle disposed radially exterior to thering of inner light baffles and further disposed between the ring ofinner light baffles and the primary and secondary baffle arrays, whereinthe outer baffle also extends from the housing structure and is shorterthan the inner baffle.
 14. The apparatus of claim 13, wherein each ofthe inner light baffles of the ring of inner light baffles shares acommon polar angle with one of the radial axes of the primary bafflearrays.
 15. The apparatus of claim 10, wherein the primary baffle arraysinclude eight primary baffle arrays and the secondary baffle arraysinclude eight secondary baffle arrays.
 16. The apparatus of claim 10,wherein each of the secondary axes is parallel to but offset from one ofthe radial axes of the primary baffle arrays such that the secondaryaxes do not run radially from the center of the central aperture. 17.The apparatus of claim 10, wherein the secondary axes each extendradially from the center of the central aperture.
 18. The apparatus ofclaim 17, wherein the primary baffle arrays and the secondary bafflearrays are angularly evenly spaced around the central aperture.